"The incident is under investigation to determine the facts and circumstances of the collision," the statement said.

The guided-missile destroyer collided with the Alnic MC as it headed for a routine stop in the city-state last week, leaving a gaping hole in the vessel's hull and flooding crew berths and machinery and communications rooms with water.

The pre-dawn crash sparked a multinational search and rescue operation off Singapore, but it was called off after several days, and authorities shifted their focus to flooded parts of the ship.

The incident, the fourth major accident for the US Pacific Fleet this year, has prompted the navy to begin a global review of its operations and remove Joseph Aucoin - the commander of the Seventh Fleet.

The US navy has also flagged plans for temporary and staggered pauses in operations across its global fleet to allow staff to focus on safety.

The Seventh Fleet, headquartered in Japan, operates as many as 70 ships, including the US navy's only forward-deployed aircraft carrier, and has about 140 aircraft and 20,000 sailors.